1. Field of the Invention (Technical Field)
The present invention relates to the recovery of nitramines form surplus energetic materials, and their reformulation into useful products.
2. Background Art
The U.S. military has stockpiled thousands of tons of surplus energetic materials that are now obsolete and either will not or cannot be used for future applications. Reduction of this obsolete surplus is of economic and environmental necessity. However, the traditional means of open burning, open detonation or dumping are not acceptable. They yield no useable materials, contribute to pollution and increase disposal site remediation costs. Two of the major components in many of these energetic materials are cyclotetramethylene tetranitramine (HMX) and cyclotetramethylene trinitramine (RDX). These compounds have the potential to be recovered from the energetic material surplus in a demilitarization method, and used as blasting agents that are booster-sensitive but not blasting cap-sensitive, nutrient additives for fertilizer, explosive metal bonding, and used in well perforating charges. On an economic basis, demilitarization to produce purified nitramines is preferable to mere reuse as blasting agentsxe2x80x94gross income from the sale of the processed HMX is on the order of a magnitude greater than that from the sale of the surplus for reuse as is.
Various chemical demilitarization methods have been proposed, but involve the use of organic solvents which result in hazardous waste. For example, U.S. Pat. No. 5,523,517, entitled Destruction of Nitramines Employing Aqueous Dispersion of Metal Powders to Cannizzo et. al. uses metal salts, which must be separated and properly disposed of, and U.S. Pat. No. 4,098,627, entitled Solvolytic Degradation of Pyrotechnic Materials Containing Crosslinked Polymers to Tompa et. al. uses hazardous solvents such as ethylene diamine, benzene and DMSO (dimethylsulfoxide). Neither addresses the need for producing reusable products from the demilitarization.
The continuously mounting stockpile emphasizes the need for a more cost-effective method that maintains quality of product. The cost-effectiveness depends upon capital investment (equipment), supplies, waste clean-up required, and labor. With the present need for a process that has no environmental repercussions, a method to demilitarize surplus energetic materials that results in a useable resource and yet has a zero waste stream is most advantageous. The present invention addresses this need.
The present invention is directed to a method of recovering nitramines from energetic materials and yielding an additional useful product. The preferred method comprising the steps of solubilizing the material in a nitric acid solution, removing the effluent to yield a nitramine, neutralizing the effluent with a base, removing the liquid content from the effluent to yield a compound salt, rinsing the nitramine, and desensitizing the nitramine.
The nitric acid solution is preferably 60-70% nitric acid, and more preferably 65-70% nitric acid. The steps of solubilizing and stirring are preferably conducted at ambient temperature. After solubilization, the solution may be heated, preferably to a temperature between 40-80xc2x0 C., and more preferably to at least 70xc2x0 C. The effluent is removed preferably by centrifuging or filtering. The effluent is preferably neutralized with ammonium hydroxide, and more preferably with at least 26% ammonium hydroxide, to neutralize preferably to a pH of approximately 6.8. The compound salt yielded from evaporation is preferably ammonium nitrate polymeric fuel (ANPF).
The nitramine is preferably rinsed with water, and desensitized preferably with alcohol, and more preferably isopropyl alcohol, added to a total liquid content of 20 w %. The method preferably yields cyclotetramethylene tetranitramine.
The invention is also directed to a method of recovering nitramines from energetic materials comprising providing an energetic material, forming a solution, adding a substance to increase density of the solution, and separating the solution into a wax component and a nitramine-containing component.
In the preferred embodiment, the energetic material provided is a compound containing a nitramine, and preferably cyclotetramethylene trinitramine. The solution is formed preferably by adding water, preferably to form a water to material ratio of between 3:1 and 7:1, and more preferably of at least 5:1. The substance added to increase density is preferably a salt, and more preferably CaCl2. The substance may also be sodium chloride, sodium bicarbonate, potassium nitrate or a sulfate. The density is increased to between 1.1 and 1.7 g/cc, and preferably to approximately 1.2 g/cc. The solution may be heated, preferably to 80-85xc2x0 C. A surfactant may be added. The surfactant added is preferably resistant to high temperatures and high acidity, and is more preferably Tween 20. The solution is preferably cooled to a maximum of 70xc2x0 C. A preferred embodiment of the invention involves separation by skimming the wax substance from the top of the solution, and aspirating the solution to leave the nitramine. The product left after aspiration is preferably cyclotetramethylene trinitramine, which is then preferably rinsed.
A primary object of the present invention is to provide a method for demilitarization of surplus energetic materials that generates value-added products.
Another object of the present invention is to provide a method for demilitarization that results in a zero waste stream.
Another object of the present invention is to provide a method for demilitarization that is less costly.
Another object of the present invention is to provide a method of demilitarization that addresses the need of a diverse surplus industry.
Another object of the present invention is to provide a method of demilitarization that relies upon disparate densities for separation of compounds.
A primary advantage of the present invention is the lack of hazardous waste of which to dispose.
Another advantage of the present invention is the use of inexpensive and readily available resources in the demilitarization process.
Another advantage of the present invention is the production of value-added products of high quality.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
The present invention is a demilitarization method of recovering nitramines, particularly HMX (cyclotetramethylene tetranitramine) and RDX (cyclotetramethylene trinitramine) from energetic materials. The energetic materials include HMX -containing compounds such as LX-14, VTG-5A, and WAY, and RDX-containing compounds such as Comp-A3. The method comprises the following steps: The energetic material is solubilized in a nitric acid solution. This solution is preferably 60-70% nitric acid, and more preferably 65-70% nitric acid. A preferred solvent to feed ratio was 0.5:1 l/kg, and a most preferred ratio is 1.0:1.0. The solubilization can take place at ambient temperature. The mixture is then heated to between 40-80xc2x0 C., and preferably to approximately 70xc2x0 C. The heat is needed to recover the HMX from the slurry, and further solubilize the oxidized binder and completely remove it from the HMX. If heat is added at the beginning, the processing time is decreased. However, the longer the heating time, the more nitric acid required.
After heating, the solution is either centrifuged or filtered to remove the effluent. The remaining substance is a nitramine, with particle size and morphology unaffected.
The resulting particles are round. Rounded particles are important for reuse applicationsxe2x80x94they blend readily, and have less sensitivity to shock and mechanical stimuli.
The nitramine is rinsed, preferably with water to minimize waste, and then is desensitized with an alcohol, preferably isopropyl alcohol, to prepare for shipping or storage. The alcohol content should bring the nitramine to a total liquid content of 20% by weight.
The effluent that is removed from the nitramine is neutralized with 26-30% ammonium hydroxide to a pH of approximately 6.8. The water content is evaporated off, and the remaining compound is ANPF (ammonium nitrate polymeric fuel), a useable by-product.
Another method for recovering nitramines form energetic materials involves extraction of RDX from RDX-containing compounds. The method relies upon disparate densities of the binder and RDX to accomplish the separation. The method comprises adding water to the energetic material to form a solution. The water to material ratio should be from 3:1 to 7:1, and preferably be 5:1 by weight
The density of the solution is then increased to between 1.1-1.7, and preferably to approximately 1.2, by the addition of a salt. This salt is preferably calcium chloride due to its ease of disposability. However, the salt may also be sodium chloride, sodium bicarbonate, potassium nitrate, or a sulfate. The increased density allows for the wax to separate from the nitramine physicallyxe2x80x94the nitramine has a heavier density and sinks, while the wax has a lighter density and floats. The solution is heated to between 80-85xc2x0 C. in the presence of a surfactant that can withstand high temperatures and an acid environment, such as Tween 20(trademark) (ICI Americas, Inc, Edinburgh, Scotland). The surfactant facilitates the heat transfer to the wax. The solution is then cooled to a temperature at or below 70xc2x0 C. to coagulate the wax at the surface. The wax is then skimmed off the top, and the solution is aspirated to leave the nitramine. The nitramine is rinsed to purify.